Re: [PATCH v2 00/21] ipmi: Allow raw access to KCS devices

[Corey Minyard <minyard@acm.org>]

On Thu, Apr 08, 2021 at 10:27:46AM +0930, Andrew Jeffery wrote:
> Hi Corey,
> 
> On Fri, 19 Mar 2021, at 16:49, Andrew Jeffery wrote:
> > Hello,
> > 
> > This series is a bit of a mix of things, but its primary purpose is to
> > expose BMC KCS IPMI devices to userspace in a way that enables userspace
> > to talk to host firmware using protocols that are not IPMI.
> > 
> > v1 can be found here:
> > 
> > https://lore.kernel.org/openbmc/20210219142523.3464540-1-andrew@aj.id.au/
> > 
> > Changes in v2 include:
> > 
> > * A rebase onto v5.12-rc2
> > * Incorporation of off-list feedback on SerIRQ configuration from
> >   Chiawei
> > * Further validation on hardware for ASPEED KCS devices 2, 3 and 4
> > * Lifting the existing single-open constraint of the IPMI chardev
> > * Fixes addressing Rob's feedback on the conversion of the ASPEED KCS
> >   binding to dt-schema
> > * Fixes addressing Rob's feedback on the new aspeed,lpc-interrupts
> >   property definition for the ASPEED KCS binding
> > 
> > A new chardev device is added whose implementation exposes the Input
> > Data Register (IDR), Output Data Register (ODR) and Status Register
> > (STR) via read() and write(), and implements poll() for event
> > monitoring.
> > 
> > The existing /dev/ipmi-kcs* chardev interface exposes the KCS devices in
> > a way which encoded the IPMI protocol in its behaviour. However, as
> > LPC[0] KCS devices give us bi-directional interrupts between the host
> > and a BMC with both a data and status byte, they are useful for purposes
> > beyond IPMI.
> > 
> > As a concrete example, libmctp[1] implements a vendor-defined MCTP[2]
> > binding using a combination of LPC Firmware cycles for bulk data
> > transfer and a KCS device via LPC IO cycles for out-of-band protocol
> > control messages[3]. This gives a throughput improvement over the
> > standard KCS binding[4] while continuing to exploit the ease of setup of
> > the LPC bus for early boot firmware on the host processor.
> > 
> > The series takes a bit of a winding path to achieve its aim:
> > 
> > 1. It begins with patches 1-5 put together by Chia-Wei, which I've
> > rebased on v5.12-rc2. These fix the ASPEED LPC bindings and other
> > non-KCS LPC-related ASPEED device drivers in a way that enables the
> > SerIRQ patches at the end of the series. With Joel's review I'm hoping
> > these 5 can go through the aspeed tree, and that the rest can go through
> > the IPMI tree.
> > 
> > 2. Next, patches 6-13 fairly heavily refactor the KCS support in the
> > IPMI part of the tree, re-architecting things such that it's possible to
> > support multiple chardev implementations sitting on top of the ASPEED
> > and Nuvoton device drivers. However, the KCS code didn't really have
> > great separation of concerns as it stood, so even if we disregard the
> > multiple-chardev support I think the cleanups are worthwhile.
> > 
> > 3. Patch 14 adds some interrupt management capabilities to the KCS
> > device drivers in preparation for patch 16, which introduces the new
> > "raw" KCS device interface. I'm not stoked about the device name/path,
> > so if people are looking to bikeshed something then feel free to lay
> > into that.
> > 
> > 4. The remaining patches switch the ASPEED KCS devicetree binding to
> > dt-schema, add a new interrupt property to describe the SerIRQ behaviour
> > of the device and finally clean up Serial IRQ support in the ASPEED KCS
> > driver.
> > 
> > Rob: The dt-binding patches still come before the relevant driver
> > changes, I tried to keep the two close together in the series, hence the
> > bindings changes not being patches 1 and 2.
> > 
> > I've exercised the series under qemu with the rainier-bmc machine plus
> > additional patches for KCS support[5]. I've also substituted this series in
> > place of a hacky out-of-tree driver that we've been using for the
> > libmctp stack and successfully booted the host processor under our
> > internal full-platform simulation tools for a Rainier system.
> > 
> > Note that this work touches the Nuvoton driver as well as ASPEED's, but
> > I don't have the capability to test those changes or the IPMI chardev
> > path. Tested-by tags would be much appreciated if you can exercise one
> > or both.
> > 
> > Please review!
> 
> Unfortunately the cover letter got detached from the rest of the series.
> 
> Any chance you can take a look at the patches?

There were some minor concerns that were unanswered, and there really
was no review by others for many of the patches.

I would like this patch set, it makes some good cleanups.  But I would
like some more review and testing by others, if possible.  I'm fairly
sure it has already been done, it just needs to be documented.

-corey

> 
> https://lore.kernel.org/linux-arm-kernel/20210319062752.145730-1-andrew@aj.id.au/
> 
> Cheers,
> 
> Andrew